Ecular weight linear polymers process for the production of technical endless filaments of high mol

ABSTRACT

Process for production of endless filaments from high molecular weight polymers having improved properties of low Eta intr. loss, and few capillary breaks per 10 Km, in a melt spinning process wherein the polymer melt is supplied to a spinning beam at high pressure, the melt is thereafter passed through a flow path constriction which effects a pressure drop of from 150 to 1200 atmospheres and a melt enthalpy increase sufficient to internally heat each of the melt particles uniformly and independently of their position in the melt flow cross section, and thereafter maintaining the increased temperature of the melt by heating all the surfaces thereafter contacted by the melt.

United States Patent [191 Riggert [451 Sept. 11, 1973 l PROCESS FOR THE PRODUCTION OF TECHNICAL ENDLESS FILAMENTS 0F HIGH-MOLECULAR WEIGHT LINEAR POLYMERS [75] Inventor: Karlheinz Riggert, Oberstedten/Ts.,

Germany 22 Filed: July 24, 1970 21 Appl. No.: 58,054

[30] Foreign Application Priority Data Dec. 22, 1969 Germany P 19 64 051.8

[52] US. Cl 264/176 F, 264/169 [51] Int. Cl B28b 3/20 [58] Field of Search 264/176 F, 169; 18/85 E, 8 SF, 8 P, 125 E, 125 B; 425/207 [56 1 References Cited 1 UNITED STATES PATENTS 3,171,160 3/1965 Moyer 425/207 3,480,997 12/1969 List 425/207 3,104,419 9/1963 LaFOrge 18/8 SF 3,197,533 7/1965 Robinson et a1. 264/176 R 3,479,692 1 1/1969 Biggelaar 18/8 SF 3,506,753 4/1970 Flammand 264/176 F 3,524,221 8/1970 .lones 18/8 SF 2,262,989 ll/194l Conklin et a1. 264/175 3,130,448 4/1964 Tomlinson 264/176 F 3,360,597 12/1967 Jones et a1..... 264/176 F 2,469,999 5/1949 Stober 264/176 F 3,437,725 4/1969 Pierce 264/176 F 3,457,342 7/1969 Parr et a1. 264/171 3,480,706 11/1969 Carpenter et al. 264/171 3,499,952 3/1970 Koliner et al. 264/171 FOREIGN PATENTS OR APPLICATIONS 618,663 3/1961 ltaly 264/176 F Primary Examiner-Jay H. Woo Attorney-Molinare, Allegretti, Newitt and Witcoff [57] ABSTRACT Process for production of endless filaments fromhigh molecular weight polymers having improved properties of lown loss, and few capillary breaks per '10 Km, in a melt spinning process wherein the polymer melt is supplied to a spinning beam at high pressure, the melt is thereafter passed through a flow path constriction which effects apressure drop of from 150 to 1200 atmospheres and a melt enthalpy increase sufficient to internally heat each of the melt particles uniformly and independently of their position in the melt flow cross section, and thereafter maintaining the increased temperature of the melt by heating all the surfaces thereafter contacted by the melt.

8 Claims, 2 Drawing Figures Patented Sept. '11; 1973 3,758,658

PROCESS FOR THE PRODUCTION OF TECHNICAL ENDLESS FILAMENTS OF HIGH-MOLECULAR WEIGHT LINEAR POLYMERS BACKGROUND OF THE INVENTION The invention relates to a process for the production of so-called technical filaments and threads (yarns) of high-molecular weight linear polymers, in particular polyesters, according to an improved melt-spinning process.

An important area of use of such technical endless filaments is the production of tire cord. A number of high polymers are well suited for this utility, especially polyesters, polyamides, and their well known modifications. Such high polymers behave similarly with respect to the considerations with which this invention is concerned, i.e., at spinning temperature these polymers tend either to a state of decomposition or to after-polymerization. The processing of any high polymers exhibiting such tendencies into technical endless filaments therefore lies generally within the scope of the present invention, although in the following description reference will be made particularly to filaments of polyethyleneterephthalate.'

Since tire cord and the inlays formed of it are among the essential construction elements for the safety and useful life ofa tire, high quality requirements are new-- rally placed on such endless filaments. In view of the alternating stretching and compression stresses which tires in operation experience, a necessary precondition for the use of synthetic filaments for tire cord is an adequate fatigue resistance of the filaments. As is well known, the fatigue resistance increases with themean molecular weight of the polymer. From this, it is desirable to produce filaments with as high as possible molecular weight.

Polyethylene terephthalate has come into strong prominence in the last few years for use in tire cord production. Polyethylene terephthalate unfortunately undergoes a considerable thermal decomposition between the conclusion of the production of the spinning raw material (raw polymer melt) and its subsequent shaping into threads. This thermal decomposition increases appreciably as the molar weight of the spinning raw material rises, and in the case of filament formation from polymer chips -5 cannot be prevented even by an intensive drying of the spinning raw material. Be-

cause of the thermal decomposition problem, the increase in the molecular weight of the spinning rawmaterial which is entirely possiblewith.polymerforming processes of today can only in part bepassed on to the spun filaments or thread formed therefrom. This thermal decomposition can be reduced, to be sure, if the molten spinning raw material is maintained for as short a time and as low a temperature as possible. However,

the residence time of the spinning melt in the spinning v ing temperature is required in the interest of a low decomposition, and on the other hand, high spinning temperature is required for trouble-free spinning. The solution of these problems was attempted by the proposal described in German published application 1,292,306. There the melt was supplied at a temperature below the spinning temperature, and then the melt was heated to the spinning temperature before the filament formation. This was sought to be achieved by an arrangement in whichthe heating box of the meltspinning device is subdivided into two heating sections by a partition provided between the spinning pump block and the spinning head, with the heating medium being separately supplied to each section. To be sure, this proposal permits in theory separate, differentiated temperature conduction within the spinning apparatus. However, due to the relatively short residence time of the melt in the higher temperature zone and the unavoidable laminarity of flow' of the highly viscous melt, the melt is not uniformly heated to the spinning temperature over the flow cross section. The undesirable conse quence is inhomogeneity of the filaments over the cross section of the spinning nozzle plate, especially where the/nozzle plate has a relatively large number'of holes. It is among the objects of the present invention to avoid these disadvantages, and in particular, to attain a rapid, uniform heating of the melt over the flow cross section before the spinning. In general terms, it is another object of the present invention to keep the loss of the high molecular weight achieved by a progressive polymer-formation process as low aspossible in the caseof rapidly decomposing high polymers. It is another object to pass the high molecular weight on to the filaments without spinning difficultiesmrin the case of strongly after-polymerizing high polymers, to keep the rise in the molecular weight as low as possible.

The-process of theinvention solves the above problems by heatingthe melt prior to spinning by pressure decrease by means of a flow path construction, and then maintaining the melt temperature level by corresponding heating of all the surfaces touched by the melt before the final spinning.

The process of this invention results in an ideally uniform temperature'increase over the full flow cross section by energy transformation at the choke point during the pressure decrease, in which each melt particle undergoes an equally great enthalpy increase, or tempering independently of its position in the flow cross section. According to the invention it isassured that this .tempering', state cannot be lost through heat lead-off byproviding a simultaneous, corresponding heating' of apparatus is unfortunately prescribed by the dimensions of the apparatus, and the lower limit of the spinning temperature is determined by the highly undesirable eondition of melt fracture. Where melt fracture occurs, the spun, unstretched filaments do not have a smooth or even surface, and exhibit fluctuations in diameter which are unacceptable for use as technical yarn, like tire cord.

It is evident from this that the spinning requirements are diametrically opposed. On the one hand, low meltthe spinning apparatus surfaces contacted by the melt. Characteristicofthis invention is that heating by means of an externalheat supply is obviated. In other words, what is characteristic of this invention is the utilization of an energy transformation for the-direct, brief, and

uniform internal heating of the melt, in which the amount of heat required for that purpose arises within the melt itself. This requires a higher spinning pump The threads of yarns produced according to the invention consist of filaments which are distinguished by a low scatter of both the diameter and the double refraction as measured over the thread cross section, i.e., low variation in these values from filament to filament. As a result, further processing propertires are excellent. Thus, by means of a one-stage or several-stage stretching process, there can be achieved yarns or threads of high tensile strength having a low filament capillary breakage number. Furthermore, the filaments show only a relatively slight decrease in the molecular weight as compared to the spinning raw material.

In the production of technical endless filaments of polyethylene terephthalate, it has been found especially advantageous if the following conditions are met: 1) the high molecular weight melt is supplied at a temperature T between 280 and 330 C., and 2) is exposed to a pressure drop or pressure gradient, Ap, between I50 and 1200 atmospheres, at the earliest after 50 percent of its residence time between melt generation and spinning, and 3) the surface temperature, T of all the surfaces contacted by the melt after the pressure drop is maintained within the following limits:

As the above limit formulas make clear, T depends on the height of the pressure gradient (drop) and the temperature T of the melt before the pressure drop. Preferably, the polyethylene terephthalate melt is supplied at a temperature T, between 285 and 310 C., and is exposed to a pressure drop (gradient) Ap between 200 and 800 atmospheres.

It is advantageous if the pressure decrease is carried out in the flow path between spinning pump and spinning nozzle plate. Good results are achieved in the finished filaments or threads especially when the pressure drop is located in the vicinity of the spinning nozzle plate. An especially simple and effective manner of carrying out the process of this invention is in providiilg that the pressure drop takes place substantially at the spinning filter, which in spinning devices in general is placed in the upper part of the so-called spinning nozzle pack. Metal sieves having l0,000 to 50,000 meshes/cm are well suited as spinning filter'material for this purpose. Such sieves can be stratified in several layers one over another and are suitably supported against the high spinning pump pressure. Sintered metal filters have also proved usable for this purpose.

In principle, the pressure decrease can be carried out according to three methods or combinations thereof in the spinning apparatus. Besides the use of spinning filter as the main choke zone for achieving the pressure drop, there can be used secondly, if need be, also the filter supporting plate, or, third, the nozzle plate bores. In the case of the supporting plate and/or nozzle bores, bores with a large length/diameter ratio, l/d, are required to achieve the pressure drop required in this invention. However, unlimited l/d ratios are not possible, at least for the nozzle bores, principally for reasons of manufacturing technology. For example, diameters of less than 1mm, very common for this spinning technology, cannot be manufactured with adequate precision where the l/d ratio is above 20. In addition, large l/d ratios are expensive to manufacture. Therefore, ac cording to the process of this invention, the pressure is brought down preferably and largely at the spinning filter. Letting pressure down at the spinning filter is also preferable because there the temperature distribution in the melt is more uniform.

In the execution of the process of the invention, it is possible to proceed both from polymer chips, which, in a known manner, are melted up on grids or by means of extruder devices, and also directly from a polymer melt obtained directly after the conclusion of the polymerization or polycondensation. In either case, short feed paths between melt discharge and spinning device are recommended. The process of the invention is particularly adapted to the processing of polymers having spinning melt solution viscosities, m equal or greater than 0.85, and preferably equal to or greater than 0.92.

In the drawings there is shown a spinning apparatus example suited for the process of the invention, in two schematic representations.

FIG. 1 represents a section througha spinning position of a spinning beam.

FIG. 2 shows a six-position-beam in a rear view.

Referring now to FIG. 1, within the self-supporting and thermally insulating beam body 1 (which is crosshatched), there are provided for each spinning position a high-pressure spinning pump 2, normally a gear wheel type metering pump, having product inlet line 3 and product outlet line 4, as well as a spinning head,generally designated as 5. The spinning head 5, in the present examp le,.being substantially rotationally symmetrical, consists of a feed plate 6 and a spinning nozzle pack holder 7 screwed together with it from above (not shown); The feedplate 6 has a radially-outward directed product inlet line 8 aligned with the product out-' let line 4, which product inlet line 8 expands conically downward to about the diameter of the spinning nozzle pack. The spinningnozzle pack comprises: a. the spinning nozzle plate 9 provided with a-large number of nozzle bores, which plate is seated on an inwardly-directed ring shoulder 10 of theholder 7, b. a filter support plate 11 resting on the plate 9, and c. the filter 12 sandwiched between supporting plate 11 and feed plate 6. The filter in this embodiment consists of a plurality of edge-framed wire gauze layers. The filter 12 has a double function: On the one hand it filtersthe spinning melt in a known manner, and on the other hand, with respect to its ,fl ow resistance, it is dimensioned in such a way that it brings about the main-proportion of the desired pressure drop.

The spinning ,pump 2 isv surrounded by a heating jacket 13, which is heated by any convenient heat transfer medium, for example the mixture of diphenyl ing tube 15 is closed by an insulating plug 17. Prefera-v I to 3mm in width, to ensure even heat transfer from vessel 14 to the head by radiation and convection.

FIG. 2 shows that the product lines 19 are adapted to have equal length between a central supply place 18 and the individual spinning pumps 2, so that the melt has a uniform residence time for all thespinning positions. The reference number 20 designates the spinning pump drive shafts.

The process of the invention is explained in detail in the following with the aid of seven examples, of which the Example 1 describes a conventional technique not according to this invention, operating without appreciable pressure drop and without temperature rise before the spinning.

Examples 2, 5 and 7 relate to the process of this invention and clearly show its advantages.

Examples 3, 4 and 6 relate to processes in which not all the features of this invention are present simultaneously, or the work is done according to the state of technology. The solution viscosity is given in the examples as the measure for the mean molecular weight, which was determined as the m value by standard procedures. The concentration of the measuring solution amounted to 0.5 g/l0.0 ml., the solvent is a phenoltetrachloroethane mixture (60 40) and the measuring temperature was C. In the examples, the diameter fluctuations along an unstretched thread filament serve as the measure of the melt fracture. The diameter fluctuations are recorded as the variation coefficient (CV value) in percentages. In some examples also the variation coefficient of the double refraction (CV, value) is given in percentages.

EXAMPLE I (Conventional Technique) A; A melt of polyethylene terephthalate having a solution viscosity of m 1.04 was supplied at a temperature'T of 310 C. to a six-position spinning beam. All the product lines, including spinning pump and spinning nozzle pack, were heated to T 310 C. The

pressure drop in the spinning nozzle filter amounted to 80 atmospheres. From a spinning nozzle plate having 200 holes, each of 0.4 mm diameter, there was gener: ated a thread with a spinning denier of 5900 den. at a draw-off speed of 400 m/min.'The solidification of the spun thread was delayed in known manner by an afterheater, in order to preclude any undesirably great molecular pre-orientation. The mean CV,, value of the unstretched thread filaments was foundtobe 4.8 percent, which indicates a spinning free of melt-fracture. After stretching the resultant cord base thread in a ratio of l 6.l, there was found to be 20 capillary breaks per 10,000 meters and a tensile strength of 9.0 g/den. Of great disadvantage was the severe drop of the solution fracture. In this case, the mean CV value of the thread filaments rose to 17 percent, while the solution viscosity in the thread was to 0.95.

EXAMPLE 2 (The Invention) The initial procedure as in Example 1 was fillowed, but with the modification that the polymer was supplied to the spinning beam, at T 292 C. instead of at 310 C. The spinning beam, including spinning pump, was likewise heated to T, 292 C. The melt residence time during its conveyance from the place of generation to the spinning beam was the same as in Example 1. In contrast to Example 1, the spinning nozzle pack was heated to a-temperature of T 310 C. By use of a spinning nozzle filter consisting of a sieve filter combination of 24 metal screen layers each having 17,000 meshes/cm, the pressure drop, Ap, was 320 at- I mospheres. The temperature of the spinning nozzle pack was therefore within the temperature range according to the invention. Using the spinning nozzle plate described in Example 1, a thread having spinning titerof 5900 denier was spun, again at 400 m/min.

draw-off speed. The mean CV value of the thread filaments was 4.6 percent. In agreement with Example I, the thread had 25 breaks per 10,000 m, which is within the measurement error limits. As compared to Example 1, the molecular decomposition of the polymer was significantly improved, being considerably less under the process parameters of the invention, the thread having a solution viscosity of m 0.94.

EXAMPLE 3 (Comparison) Example 2.

EXAMPLE4 a (Comparison) Initially, the same procedure as in Example 2-was' followed, with the modificationthat the spinningjnozzle pack was heated to a temperature T, of 325 C. This temperature T, lies outside the range according to this invention. The m value of the thread was 0.93 which is only=a little lower than in Example 2. Although under these process conditions no melt fracture occurred,the

CV valuewas 10 percent, as a result of the temperature inhomogeneity of the melt emerging from the spinviscosity of the thread, which was found to be m thread material obtained was no longer faultlessly' spinnable and stretchable because of setting in of melt ning nozzle plate. For the'same reason, the CV, value amounted to 15 percent, and as a consequence the capillary break frequency was considerable. With respect to a thread tensile strength of 9.0 g/den. I00 capillary breaks per l0,000 m were counted.

EXAMPLE 6 (Comparison) EXAMPLES EXAMPLE 7 (The Invention) (The Invention) 1 cosities (m A and m the viscosity decrease A m the CV value and, in some cases the CV, value. The advantages of working with the technique described in the present invention are easily seen by a 8 thread. 2. A process as in claim 1 wherein said polymer is a polyester.

3. A process as in claim 2 wherein:

comparison of the values for the viscosity decrease, 5 a i polyester is polyethylene terephthalate, and/or for alid/01' for the capillary break b. said pressure drop is effected at the earliest after bers. For the sake of better comparison, values for Ex- 0 percent of the total melt residence time between amples 1 to 4 were also included in the table. generation and Spinning and IATBLTT f number for GVD, CV, lntrA lntrE Aqll'ltl Km. percent percent Corresponding state of technology 1.04 0.86 0.18 4.8 Prior art.

1.04 0.94 0.10 4.6 6.8 The invention.

1. 04 0.95 0. 09 120 12. 0 10.0 Process not according to the invention.

1. 04 0. 93 o. 11 100 10.0 15. 0 Do.

0.96 0.87 0.09 22 4.7 7.2 The invention.

0.06 0.89 0.07 1 16.0 Process not according to the invention.

1. 08 0.95 0.12 27 4.5 7.0 The invention.

1 Melt fracture not perfectly splnnablc and stretchable.

What is claimed is: c. the temperature, T of all of said surfaces touched 1. In a process for the production of industrial monoby said melt after said pressure drop is maintained filaments from high-molecular weight thermoplastic 30 ithi th f ll i li it polymers selected from linear polyester and polyamide polymers by melt-spinning, which high polymers are subject to decomposition or after-polymerization at spinning temperatures, including the steps of supplying a melt of said polymer at a temperature below the spin- T a T 2 nin tem erature, and heatin the melt rior to the fila- 1 5 T 1 mest forr iiation, the improve ment whicfh comprises: T [(l7+l0 3) (M7)] T [1O( a. supplying said melt at a temperature T between 100 280 and 330 C and at high pressure to a spinning unit comprising a spinning pump, a nozzle plate and construction means disposed between said pump and said nozzle plate,

Passing Said melt y means of Said spinning P p ifA process as in Claim 3 wherein said polyethylene through a constriction in its flow path said constricte ephthalate melt is supplied at a temperature T be tion occurring within said constricting means prior tween 2 5 and 310* Cu and the pressure drop, A p, is to said melt passing through said spinning nozzle between 200 d 00 atmospheres 1 Plate to effect a Pressure p P o between 150 5. A process as in claim I wherein said polymer is and 1200 atmospheres before arrival of said melt li d at a temperature, T between 235 and 310 at said spinning nozzle, and an increase of the inter- C and h pressure drop, A i between 200 and 300 nal energy sufficient to internally heat the melt to atmospheres I a temperature greater than T which increased 6 A process as i claim 1 i temperature is uniform and independent of the id bl comprises a i i pump and a melt position in the flow cross section under condii i nozzle l t d tions which provide low loss of intrinsic viscosity 5 b id pressure d i eff ct d i h fl w h and (1085 not change the laminarity Of melt flOW, tween aid spinning pump and spinning nozzle c. supplying heat from the exterior to said spinning l m unit surfaces thereafter contacted by said melt in 7. A process as in claim 6 wherein said assembly i an amount only sufficient to maintain the increased l d a i i filter di d upstream f said temperature of said internally heated melt but i zle plate, and said pressure drop is effected principally sufficient to cause substantial thermal degradation atsaid spinning filter. or after polymerization, and 8. A process as in claim 7 wherein:

d. spinning filaments from said melt, said filaments a. said polymer is polyethylene terephthalate,

exhibiting improved properties of low m,,,,, loss, 'b. said pressure drop is effected at the earliest after low diameter and double refraction variation coef- 50 percent of the total melt residence time between ficients, and few filament breaks per 10 Km. spun generation and spinning, and

c. the temperature, T of all of said surfaces touched T, T T

by said melt after said pressure drop is maintained T [(17 10 (Ap)] 2: T (Ap within the following limits: T66 

2. A process as in claim 1 wherein said polymer is a polyester.
 3. A process as in claim 2 wherein: a. said polyester is polyethylene terephthalate, b. said pressure drop is effected at the earliest after 50 percent of the total melt residence time between generation and spinning, and c. the temperature, T2, of all of said surfaces touched by said melt after said pressure drop is maintained within the following limits:
 4. A process as in Claim 3 wherein said polyethylene terephthalate melt is supplied at a temperature, T1, between 285 and 310* C., and the pressure drop, Delta p, is between 200 and 800 atmospheres.
 5. A process as in claim 1 wherein said polymer is supplied at a temperature, T1, between 285 and 310* C., and the pressure drop, Delta p, is between 200 and 800 atmospheres.
 6. A process as in claim 1 wherein: a. said assembly comprises a spinning pump and a spinning nozzle plate, and b. said pressure drop is effected in the flow path between said spinning pump and spinning nozzle plate.
 7. A process as in claim 6 wherein said assembly includes a spinning filter disposed upstream of said nozzle plate, and said pressure drop is effected principally at said spinning filter.
 8. A process as in claim 7 wherein: a. said polymer is polyethylene terephthalate, b. said pressure drop is effected at the earliest after 50 percent of the total melt residence time between generation and spinning, and c. the temperature, T2, of all of said surfaces touched by said melt after said pressure drop is maintained within the following limits: 